Japanese patent document JP H11-082260 A discloses a hybrid drive system for a hybrid vehicle. That hybrid drive system includes a motor-generator connected with a shaft between an engine and a transmission, a first clutch disposed between the engine and the motor-generator and a second clutch between the motor-generator and the transmission in place of a torque converter.
This hybrid drive system can drive the vehicle in an electric drive (EV) mode with the power only from the motor-generator by disengaging the first clutch and engaging the second clutch, and in a hybrid drive (HEV) mode with power from both the engine and motor-generator by engaging the first and second clutches.
The hybrid drive system can control the first and second clutches by using a clutch control technique such as that disclosed in Japanese Patent document JP 2004-203219 A. The clutch control system of this clutch control technique is arranged to control the engagement of the clutch by supplying an oil pressure to the clutch so as to achieve the transmission torque capacity capable of transmitting the torque generated by the power sources.